Trip-free safety switch



June 28, 1966 H. w. LANDAU 3,258,563

TRIP-FREE SAFETY SWITCH Filed May 12, 1964 [I 71 J f?) FIE 5 1-71 5'0 6'! 45 ll 5 p 62 15' [[54 1|. 59 -45 29 2.2 5'5 5'5 INVENTOR. lb. 52 A a/ yr 14/ AAA/.040

56M 51 m BY W 47 TOP V United States Patent 3,258,563 TRIP-FREE SAFETY SWITCH Horst W. Landau, Hopkins, Minm, assignor to Honeywell Inc., Minneapolis, Minn., a corporation of Delaware Filed May 12, 1964, Ser. No. 366,798 4 Claims. (Cl. 200-416) The present invention is concerned with an improved trip free manually resettable safety switch; in particular, a switch has a member which can be manually moved from a first position to a second, closed circuit, position to be held in the second position by a latch mechanism, but the switch is held in an open circuit condition as long as force is applied to a manual resetting member.

For many years switches have been available to provide a closed circuit which is opened on the presence of some predetermined undesirable condition. In order to restore the circuit to a closed position, a manual operated means is provided. Upon positioning a manual button, the switch mechanism is reset by latching the mechanism in a closed circuit position. When such switches are used for safety switches a trip free feature has been required in many cases. Trip free action of such a switch provides that the manual operator which is used to reset the switch cannot be used to hold the switch in a closed circuit condition. A dangerous and unsafe operating condition can be brought about if the manual operator of such a switch can be held in a circuit closed position by various means which maintains a force on the manual button. In order to overcome the possibility of placing equipment using such safety switches in a condition where no safety signal is available, the trip free safety switch came about. In a trip free safety switch, any force upon the manual operator of switch resetting button maintains the switch in an open circuit condition. With such la feature, a switch cannot have the reset button taped down or wedged in such a manner to keep the safety switch closed.

In the prior art, many of these switches were quite complicated with expensive linkages which resulted in a high manufacturing cost .as well as a switch design which under some conditions could be cheated to overcome the trip free action. The present invention provides for a simple and yet novel switch which can be set by means of a manual button to move a switch member to a latched position; however, upon the presence of any force on the manual operating button, the circuit of the switch is maintained open and a trip free" action is provided.

An object of the present invention is to provide a switch having a switch carrying member which is moved from a first to a second position by a force of a manual operator but having two circuit members connected by a third member the switch is maintained closed as the third member opens the switch only when no force is present.

Another object of the present invention is to provide a switch which has a contact carrying member guided to be moved from a first to a second position to be latched by a latch mechanism in the second position. A manual operator for moving the contact carrying member prevents the closure of a switch when any force is applied to a resilient U-shaped contact member of the switch by the manual operator.

These and other objects of the present invention will become apparent upon the study of the following specification and drawings of which FIGURE 1 is a front view of the safety switch with the cover cut away to show the bimetal latch mechanism and the contact carrying member in the unlatched position.

FIGURE 2 is a side cut away view of the switch of FIGURE 1 with the front cover open.

FIGURE 3 is a partial front view of the switch of FIGURE 1 with the contact carrying member completely downward as force is being applied to the manual button.

FIGURE 4 is the partial front view of the switch of FIGURE 1 with force being applied to the manual button and the contact carrying member in a latched position.

And FIGURE 5 is a partial from view of FIGURE 1 with the contact carrying member in a latched position and no force being applied to the manual button.

Referring to FIGURE 1 a switch housing or base has a back side 11 and a front cover 12. Projecting from the back 11 is a support member 13 which is an integral part of the base. A heat operated latch mechanism 14 comprises a bimetal 15 which is formed in a U-shaped to have one leg longer than the other leg 21. An extremity 22 of long leg 20 is attached to a free end of a flexible support spring 23 which has the other end 24 attached to projection 13. By means of a screw 25 threaded through one side of base 10 and engaging extremity 22 of bimetal 15, the position of the long leg 22 of bimetal 15 can be adjusted by bending spring spring 23 for calibration purposes. Mounted in the bent portion 31 of the U-shaped bimetal 15 is an electrical heater or resistor 32 which is connected by a pair of wires 33 and 34 as shown in FIGURE 2 between a pair of electrical terminals or electrical circuit contacts 35 and projecting through a lower side 41 of base v10. Bimetal 15 has a hole 42 on leg 20 half way between bent portion 31 and the extremity 22 which minimizes the transfer of heat from heater 32 to the far end of the long leg 20 passed hole 42. A notch 43 in the short leg 21 provides a latch means for a projection 44 on a switch contact carrying member or housing 45.

Bimetal 15 is designed so that upon the application of heat to the bimetal by heater 32, the outer layer of the bimetal expands faster than the inner layer to result in a cloclcwise movement of leg 21 with respect to leg 20 of the bimetal. By means of the additional length of leg 20, the electrical actuator '14 is compensated for any changes in ambient temperature .as upon a change in ambient temperature, .the portion 20 of bimetal moves to reposition the short leg 21. Since the upper portion 20 of the long leg is for ambient compensation, any heat from the heater 32 is minimized from flowing up through the bimetal by means of hole 42.

Another pair of terminals and 51 are mounted in lower side 41 of base 10 to extend upward into the inner chamber of base 10 to provide a pair of switch contacts or members 52 and 53 respectively. Contact carrying member 45 is guided on members 52 and 53 to allow free movement of member 45 from a first position as shown in FIGURE 1 to a second position as shown in FIGURE 5. Member 45 is biased upward away from lower side 41 of the base by a compression spring 54 which has one end received on a projection 55 of contact carrying member 45. Mounted inside contact carrying member 45 is a U-sha-ped electrical circuit member or spring contact 59 which has two extremities 61 and 62 which are positioned depending upon the force applied to a center portion 63. A pair of inwardly projected space members 64 and 65 which are molded integrally with the contact carrying member hold the U-shaped contact or contact spring 59 in position and provided for a bending surface to result in the movement of extremities 61 and 62 when force is applied to a center portion 63 to spring 59.

A manual operator has a button 71 protruding from the supper side 72 of base 10. A projection 73 connected to the manual operator passes through a notch in the contact carrying member 45 to a position between the extremities 61 and 62 of contact 59 to engage portion 63 of the contact 59.

A pair of triangular shaped projections inside contact carrying member 45 bare against opposite sides of said 3 U-shaped contact 59 whereby upon projection 73 pressing on center portion 63, extremities 61 and 62 move together away from contacts 52 and 53 when contact carrying member 45 has moved downward to have contacts 52 and 53 adjacent extremities 61 and 62.

When member 45 is in the upper most position beyond the extremities of contacts 52 and 53 contact 59 cannot complete electrical circuit between terminals 50 and 51.

A resilient contact member 80 as shown in FIGURES 1 and 2 is carried in a hole on the front side of contact carrying member 45. Member 80 cooperates with a plurality of conductor strips 81, 82 and 83 on the inner surface of cover 12 to provide a switch for controlling a circuit connected to terminals 85, 90 and 1 depending upon the position of contact carrying member 45.

Operation As shown in FIGURE 1, the safety switch is in the unlatched or first position. Contact carrying member 45 has been released and is moved upward to the first position under the force of spring 54. The extremities 61 and 62 of switch member 59 are fully extended but since the extremities are above the ends of extremities of contacts 52 and 53, a closed circuit does not exist between terminals 50 and 51..

In order to reset the switch, a force F is applied to the upper end of button 71 to push member 45 downward to compress spring 54 as shown in FIGURE 3. Projection 44 have been moved past the short leg 21 of bimetal and by means of the upper end 95 of leg 21, downward movement of projection 45 causes the bimetal to bend clockwise so projection 44 can pass the bimetal into the position as shown in FIGURE 3. As long as force is applied to the upper surface of button 71 contact 59 is warped so that extremities 61 and 62 are pulled together and contacts 52 and 53 are not engaged. As shown in FIGURE 3, member 45 is below the latched position and upon the release of force from button 71, member 45 will move upward to the position as shown in FIGURE 4 with projection 45 in notch 43 of short leg 21 of bimetal. Member 45 is then held in a second position. As long as force is applied to the upper end of button '71 as shown in FIGURE 4, spring contact 59 will be deformed and extremities 61 and 62 are pulled together to not engage contacts 52 and 53 to maintain the circuit between termi nals 50 and 51 open.

Upon the removal of force F contact 59 springs outward so extremities 61 and 62 engage adjacent contacts 52 and 53 to establish the circuit between terminals 50 and 51 and contact carrying member 45 will remain in the latched or second position as shown in FIGURE 5 With U-shaped contact 59, any small force F applied to button 71 results in the deformation of contact 59 so extremities 61 and 62 are pulled inward away from contacts 52 and 53. A trip free safety switch is then provided which prevents closure of a control circuit connected to terminals 50 and 51 if button is held down in any way. For example, if button 71 is taped down, contact 59 would not complete an electrical circuit between terminals 50 and 51 even when switch carrying member 45 was in the second or latched position as shown in FIGURE 4.

Upon an application of voltage to terminals and 40, current is supplied to heater 32 to increase the temperature of the bimetal 15. The short leg 21 of bimetal 15 will move clockwise and the notch will release projection 44 to allow the contact carrying member to move upward under the force of spring 54. In this manner, the circuit between terminals and 51 is broken as shown in FIGURE 1. Depending upon the position of member 45, the switching action of the circuit between terminals 85, 90 and 91 can be used for various signaling and control purposes.

As the ambient temperature of surrounding base 10 changes, the temperature of bimetal 15 needed to trip latch mechanism 14 is changed. As the corresponding portions of the bimetal close to the bent portion 31 provide the active operation needed to move the short leg 21 to unlatch the contact carrying member 45, the longer portion 20 of bimetal 15 acts to move the active portion to change the level of heat needed from the heater 30 for different ambient temperatures to maintain the timing or time required for operator 14 to release the contact carrying member 45 constant.

While the present invention has been described in one particular manner, the scope of the invention is only limited by the appended claims of which I claim:

1. In a safety switch for providing trip free action, a base providing a chamber with an open side, a cover for said base, a pair of electrical current carrying contacts mounted in one side of said chamber to protrude outside said base for providing electrical circuit connections and to protrude in a parallel spaced relationship into said chamber, a movable switch contact carrying member slideably connected to said contacts so said member can move between a first and a second position, a manual operating button extending through one side of said base into said chamber and adapted to move said member from said first to said second position, a bimetal latch means mounted in said chamber, an electrical heater for heating said bimetal, a projection on said member, said projection being received by said latch means when said member i in said second position and said bimetal is cold, a spring biasing said member from said second to said first position whereby upon said heater heating said bimetal said latch means is tripped and said member moves to said first position, a switch means contained in said member to engage said bars when said member is moved to said second position, said switch means comprising a U-shaped resilient blade which is normally held in said member between a pair of project-ions to have free extremitie of said blade extending apart to contact said bars when said member is moved to said second position, a projection attached to said button, said projection extending into said member to engage a center portion of said U-shaped blade to move said blade against said projections to warp said blade when force is applied to said button to pull said extremities together whereby said extremities cannot contact said bars until said member is latched in said sec ond position and the force on said button is removed, circuit means mounted on said cover, and a contact carried by said member for closing said circuit means when said member is in one of said positions.

2. In a safety switch for providing trip free action, a housing, a pair of contact members mounted in said housing, a movable member guided by said contact members so said member can move between a first and a second position, a thermally operated latch means mounted in said housing an electrical heater for heating said latch means, a projection attached to said movable member, said projection being received by said latch means when said member is in said second position, means biasing said member from said second to said first position whereby upon said heater being energized said latch means is released and said member moves to said first position, a switch means contained in said member to engage said pair of contact members when said member is moved to said second position, said switch means comprising resilient blade which is normally held in said member between a pair of projections attached to said member to have two free extremities of said blade extending apart to contact said contact members when said member is moved to said second position, and a projection attached to a manual button for resetting the safety switch, said projection extending into said member to engage a center portion of said blade to move said blade against said projections to warp said blade when force is applied to said button to pull said extremities together whereby said extremities cannot contact said contact members until said member is latched in said second position and the force on said button is removed.

3. In a switch to be manually closed and latched in a closed position to be released by an electrical energized actuator in a manner to provide for closure of the switch only when a manual operator is completely released, a base, a first member movably supported on said base, a spring mounted between said member and said base to bias said member in a first position, a manual operator adapted to move said member against said spring to a second position when said operator is pushed, latch means mounted in said base said latch means being normally in a first position and upon being electrically energized being in a second position, said latch means when in said first position engaging said switch carrying member when said member is in said second position to hold said member in said position even though said manual operator is released, a pair of switch contact members mounted in said base, a resilient switch contact member having two extremities and a center portion, and means mounting said contact member in said first member so said extremities normally engage said pair of contact members, said manual operator engaging said center portion of said resilient member to bend said resilient member when a force is applied to said manual operator to move said extremities whereby upon said first member being in said second position said extremities cannot engage said pair of contact members to close a circuit between said switch contact members however after said first member is latched and force is removed from said operator said resilient contact member is released so said extremities engage said contact members to complete an electric circuit.

4. In a switch to be manually closed and latched to provide for closure of an electrical circuit only when a manual operator is completely released, a base, a first member movably supported on said base, resilient means mounted between said member and said base to bias said member in a first position, latch means mounted in said base, said latch means being normally in a latching position and upon being actuated in a second position, said latch means when in said first position engaging said first member when said member is in a second position to hold said member in said second position, a first and a second electrical circuit member mounted in said base, a third electrical circuit member, said third member having extremities, means mounting said third circuit member in said first member, said extremities normally engaging said first and second electrical circuit members to provide a closed circuit, means movable relative to said third member, and a manual operator engaging said third circuit member when a force is applied to said manual operator so said means movable moves at least one extremity of said third member to open said closed circuit between said first and said second circuit members whereby upon said first member being in said second position said circuit cannot be closed however after said first member is latched and force is removed from said operator said third circuit member closes said electrical circuit.

References ited by the Examiner UNITED STATES PATENTS 303,579 8/1884 Lungen 200-159 1,408,097 2/1922 Klein 200-159 1,859,981 4/1932 Norviel 200168 X 2,171,895 9/ 1939 Sardeson. 2,420,880 5/ 1947 Hetherington 200-159 2,541,679 2/1951 Van Auken 200116.2 2,798,918 7/ 1957 Gelzheiser 200116.1 2,842,641 7/1958 Page 200116.2 X 2,93 8,985 5/ 1960 Brantingson 200159 3,104,300 9/1963 Hutt 200-159 3,171,919 3/1965 Hammerly 20()116.2 X

FOREIGN PATENTS 587,373 11/1933 Germany. 513,143 10/ 1939 Great Britain.

BERNARD A. GILHEANY, Primary Examiner. 

1. IN A SAFETY SWITCH FOR PROVIDING "TRIP FREE" ACTION, A BASE PROVIDING A CHAMBER WITH AN OPEN SIDE, A COVER FOR SAID BASE, A PAIR OF ELECTRICAL CURRENT CARRYING CONTACTS MOUNTED IN ONE SIDE OF SAID CHAMBER TO PROTRUDE OUTSIDE SAID BASE FOR PROVIDING ELECTRICAL CIRCUIT CONNECTIONS AND TO PROTRUDE IN A PARALLEL SPACED RELATIONSHIP INTO SAID CHAMBER, A MOVABLE SWITCH CONTACT CARRYING MEMBER SLIDEABLY CONNECTED TO SAID CONTACTS SO SAID MEMBER CAN MOVE BETWEEN A FIRST AND SECOND POSITION, A MANUAL OPERATING BUTTON EXTENDING THROUGH ONE SIDE OF SAID BASE INTO SAID CHAMBER AND ADAPTED TO MOVE SAID MEMBER FROM SAID FIRST TO SAID SECOND POSITION, A BIMETAL LATCH MEANS MOUNTED IN SAID CHAMBER, AN ELECTRICAL HEATER FOR HEATING SAID BIMETAL, A PROJECTION ON SAID MEMBER, SAID PROJECTION BEING RECEIVED BY SAID LATCH MEANS WHEN SAID MEMBER IS IN SAID SECOND POSITION AND SAID BIMETAL IS COLD, A SPRING BIASING SAID MEMBER FROM SAID SECOND TO SAID FIRST POSITION WHEREBY UPON SAID HEATER HEATING SAID BIMETAL SAID LATCH MEANS IS TRIPPED AND SAID MEMBER MOVES TO SAID FIRST POSITION, A SWTICH MEANS CONTAINED IN SAID MEMBER TO ENGAGE SAID BARS WHEN SAID MEMBER IS MOVED TO SAID SECOND POSITION, SAID SWITCH MEANS COMPRISING A U-SHAPED RESILIENT BLADE WHICH IS NORMALLY HELD IN SAID MEMBER BETWEEN A PAIR OF PROJECTIONS TO HAVE FREE EXTREMITIES OF SAID BLADE EXTENDING APART TO CONTACT SAID BARS THEN SAID MEM- 